Developmental dyslexia is the most common learning disorder which affects 4% of the school-age population in the U.S. It is manifested by difficulties in single word decoding which usually reflects an insufficient skill in phonological processing. It occurs in otherwise competent individuals who have conventional instruction, adequate intelligence and sociocultural opportunities. The disease is of constitutional origin and inheritance has been established as a major etiology. We have collected more than 47 dyslexia pedigrees from the Karolinska Institute, Harvard and Yale Medical Schools for a genome-wide linkage screening to identify loci responsible for the trait. Candidate gene- based association studies with haplotype relative risk method has excluded dopamine receptor DRD4 gene's involvement in the onset of dyslexia. Work in progress includes more candidate gene studies and infrastructure buildup on replicating and condensing the Merck brain cDNA library.